1. Field of the Invention
The invention is in the field of variable magnification reproduction machines.
2. Description of the Prior Art
Variable magnification reproduction machines are known in the prior art as exemplified by U.S. Pat. Nos. 3,542,467, 3,614,574, 3,778,147, 3,884,574 and 3,897,148. In U.S. Pat. No. 3,897,148, for example, discrete values of magnification are provided in a lens scanning apparatus wherein each of a plurality of cams corresponds to a single, discrete value of magnification. In machines having scanning optical systems, the selection of a desired magnification value is generally associated with a corresponding selection of optical scanning speed and distance of travel. Such correspondence is particularly present in machines using a photoreceptive surface moving at constant speeds. In such machines, to obtain smaller magnification ratios, one generally scans a document at a faster rate and also extends the distance of travel so that a larger document may be reproduced using the available photoreceptive surface. The minimum magnification value in such machines is dictated by the platen size in the scan direction.
It is also known to switch and selectively terminate platen document scanning of constant velocity scanning means prematurely for smaller documents in a fixed magnification copier, e.g. the Xerox Corporation "1000" copier.
Extending the magnification range to include still smaller magnification values has not generally been possible because of the physical size limits on the platen and reproduction machine itself and limitations of space and cost for discrete cams as in the Xerox Corporation "7000". In particular, the combination of a relatively small or conventional platen size together with small values of magnification points toward conflicting design requirements.
One method and apparatus for extending the magnification range is disclosed in co-pending U.S. application, Ser. No. 590,906, filed June 27, 1975, the whole of which application is incorporated herein by reference. The co-pending application discloses an imaging means, such as a fixed focal length lens, which is adjusted to provide a selected magnified image of an original document on a photoreceptor surface. Cooperating with the imaging means is a cam and a follower arm whose effective radius may be varied in accordance with the selected magnification value. For values of magnification within the extended smaller range of magnifications, the document scanning means increases in velocity across the document original but the extent of travel of the scanning means is terminated at the end of the platen by means of a clutch arrangement. The clutch arrangement is automatically activated for the smaller magnification values, and is not utilized for the large magnification values.
An alternate approach to providing an extended multiple range variable magnification reproduction machine is set forth in co-pending application Ser. No. 647,941, filed Jan. 12, 1976, the whole of which application is incorporated herein by reference. In this application, a multiple cam arrangement is provided wherein, each cam provides a continuous range of magnification values without the use of a clutch mechanism.
Another approach to providing a multiple range variable magnification reproduction machine is set forth herein where the single and dual cam mechanisms used in the aforementioned copending applications are replaced by a three-dimensional cam having a continuous cam surface in the axial direction which is specifically tailored to produce the desired scanning velocities and scanning distances for the chosen magnification.